U.S. patent number 4,152,400 [Application Number 05/819,049] was granted by the patent office on 1979-05-01 for method for treating sulfur dioxide with sorbent.
This patent grant is currently assigned to Exxon Research & Engineering Co.. Invention is credited to Neville L. Cull, Martin O. Gernand, Dale D. Maness.
United States Patent |
4,152,400 |
Gernand , et al. |
May 1, 1979 |
Method for treating sulfur dioxide with sorbent
Abstract
Process for preparing shaped base materials for use in solid
catalysts for commercial processes. The solid contact material is
prepared by pre-soaking a porous solid particulate carrier material
in an organic liquid, immersing the carrier without drying in a
dilute acid solution for a given time interval, washing, drying and
calcining the impregnated carrier. After calcination, the carrier
is impregnated with an active material.
Inventors: |
Gernand; Martin O. (Baton
Rouge, LA), Maness; Dale D. (Austin, TX), Cull; Neville
L. (Baker, LA) |
Assignee: |
Exxon Research & Engineering
Co. (Florham Park, NJ)
|
Family
ID: |
24643253 |
Appl.
No.: |
05/819,049 |
Filed: |
July 26, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
658919 |
Feb 16, 1976 |
4087383 |
|
|
|
Current U.S.
Class: |
423/242.4;
423/244.04; 252/190 |
Current CPC
Class: |
B01D
53/02 (20130101); B01J 37/0207 (20130101); B01D
53/8628 (20130101); B01D 53/508 (20130101) |
Current International
Class: |
B01D
53/02 (20060101); B01D 53/50 (20060101); B01D
53/86 (20060101); B01J 37/00 (20060101); B01J
37/02 (20060101); B01J 008/00 (); C01B
017/00 () |
Field of
Search: |
;423/242,244
;252/190,463 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Vertiz; O. R.
Assistant Examiner: Heller Gregory A.
Parent Case Text
This is a division of application Ser. No. 658,919, filed Feb. 16,
1976, now U.S. Pat. No. 4,087,383.
Claims
What is claimed is:
1. A process for the removal of sulfur dioxide from a gas stream
containing sulfur dioxide and oxygen which comprises contacting
said gas stream in a reaction zone, at the sulfurization
conditions, with a particulate sorbent comprising a sorbing metal
or metal oxide or a mixture of metals or metal oxides impregnated
upon a porous, solid inorganic refractory carrier, said sorbent
prepared by a process comprising:
(a) immersing particles of said porous, solid inorganic refractory
carrier in a polar organic presoak liquid so as to substantially
completely fill the pores of the carrier, said presoak liquid being
capable of wetting the carrier and capable of displacement by the
acid etching solution used in step (c) at a rate slow enough to
permit control of the extent of acid attack;
(b) separating said carrier plus absorbed presoak liquid from said
presoak liquid;
(c) immersing said carrier in an acid solution, said acid solution
being substantially immiscible with said presoak liquid;
(d) removing said acid solution from said carrier;
(e) impregnating the acid solution treated carrier with an
impregnating solution containing a decomposable metal compound;
and
(f) drying said carrier and converting said decomposable metal
compound to said desired sorbing metal or metal oxide or a mixture
of metals or metal oxides.
2. The process of claim 1 wherein said porous solid inorganic
refractory carrier is alumina.
3. The process of claim 1 wherein said porous, solid inorganic
refractory carrier is hydrophilic.
4. The process of claim 1 wherein said sorbing metal oxide is
copper oxide.
5. The process of claim 1 wherein said presoak liquid comprises one
or more aliphatic monohydric alcohols containing 4 to 12 carbon
atoms.
6. The process of claim 1 wherein the impregnating solution
employed in step (e) is an aqueous solution.
7. The process of claim 1 wherein the acid employed in step (c) is
a water soluble acid having an ionization constant of at least
about 1.0.times.10.sup.-3.
8. The process of claim 1 wherein the acid component of the acid
solution employed in step (c) is hydrochloric acid.
9. A process for the removal of sulfur dioxide from a gas stream
containing oxygen and from 0.1 to 0.5 vol. % sulfur dioxide which
comprises passing said gas stream at a temperature of from
600.degree. to 900.degree. F. into a reaction zone and contacting
the same therein with a particulate sorbent comprising copper oxide
impregnated upon alumina at a space velocity of no more than about
10,000 volumes of said gas stream per volume of particulate sorbent
per hour, said sorbent prepared by a process comprising:
(a) immersing alumina particles in a polar organic presoak liquid
so as to substantially completely fill the pores of said alumina,
said presoak liquid being capable of wetting the alumina and
capable of displacement by the acid etching solution used in step
(c) at a rate slow enough to permit control of the extent of acid
attack;
(b) separating said alumina plus absorbed presoak liquid from said
presoak liquid;
(c) immersing said alumina in an acid solution, said acid solution
being substantially immiscible with said presoak liquid;
(d) removing said acid solution from said alumina;
(e) impregnating said acid solution treated alumina with an
impregnating solution containing a copper compound which is
decomposable to copper oxide; and
(f) drying said alumina and converting said copper compound to
copper oxide.
10. The process of claim 9 wherein said gas stream contains from 1
to 4 vol. % oxygen.
11. The process of claim 9 wherein said presoak liquid comprises
one or more aliphatic monohydric alcohols containing 4 to 12 carbon
atoms and wherein the acid employed in step (c) is hydrochloric
acid.
Description
BACKGROUND OF THE INVENTION
This invention relates to: a process for preparing improved
catalyst and sorbent supports; the supports prepared thereby;
catalysts and sorbents comprising these supports; and to processes
wherein such catalysts and sorbents are used.
Processes wherein solid contact materials, such as supported
catalysts and/or supported sorbents are used, are, of course, well
known in the prior art. These include petroleum processes such as
catalytic cracking and hydrocracking, reforming and the like and
various gas purification processes such as those involving the
catalytic conversion of nitrogen oxides in the presence of ammonia
or other reducing agent and those involving the adsorption of
sulfur oxides.
As is also well known in the prior art, the activity of many, if
not all, of these prior art catalysts and sorbents can be altered,
and often improved, by an acid treatment of the carrier or support
material either before or after the same has been shaped.
Generally, however, such acid treatment has adversely affected the
strength characteristics of the resulting catalyst or sorbent. This
is particularly true with the so-called amorphous carriers such as
alumina, silica, titania, zirconia, alumina-silica, silica-alumina
and the like. As a result, acid treatment has not heretofore, been
generally used in the preparation of catalysts and sorbents. It is,
therefore, an object of the present invention to provide a process
in which acid treatment could be used to increase the activity of
catalysts and sorbents without adversely affecting their strength
characteristics.
SUMMARY OF THE INVENTION
In accordance with the present invention, sorbents and catalysts of
improved activity are prepared. By the present method, the carrier
material is immersed in a presoak liquid and then in an acid
solution which is substantially immiscible with the presoak liquid.
Immersion in the acid solution is controlled so that the carrier
material is etched as desired. Next, the carrier material is
removed from the acid solution, washed to remove the acid, dried
and calcined. The calcined, etched carrier material is then
impregnated by immersion in an impregnating solution containing a
dissolved compound which is decomposable into a desired active
material, dried and the decomposable compound converted into the
desired active material by calcination.
DETAILED DESCRIPTION OF THE INVENTION
The sorbent preparation techniques to be described herein are
applicable generally to the preparation of porous granular solid
contact materials, particularly shaped or extruded materials,
comprising a porous carrier material and an active material which
is deposited on the carrier.
The carrier material which can be used in the preparation of
catalysts and sorbents according to this invention are porous
materials in granular or particulate form. The materials are
inorganic refractory substances, which are preferably hydrophilic
so that they can be wetted by polar organic liquids and by aqueous
impregnating solutions. Typical carrier materials include alumina,
silica, silica-alumina, titania, titania-alumina, alumina-zirconia,
alumina-thoria, bauxite, magnesia, and the like. Alumina is a
preferred carrier material for the preparation of flue gas
desulfurization sorbents, and for other catalysts and sorbents as
well.
The carrier according to the present invention is in the form of
particles or grains in any desired shape. Conventional shapes such
as spheres and cylindrical extrudants can be used. However, best
results are obtainable when the carrier particle is a more
irregular shape, such as Raschig rings or Intalox saddles, the
latter being shown and described in U.S. Pat. Nos. 2,639,909 and
3,060,503. These irregular shapes are preferred because packed beds
of these shapes have a higher void volume with resultant lower
pressure drop than packed beds of more conventional shapes such as
spheres and cylinders. The carrier materials can be formed into
particles of desired shape by known techniques such as extrusion.
It is believed, however, that such shaping techniques cause the
formation of a low porosity outer layer on the base material. This
less porous covering can significantly interfere with the ingress
and egress of fluid reactants and products, thus materially
reducing the effectiveness of the catalytic materials. In
accordance with the theory, acid treatment techniques are thought
to be effective in that they remove this layer.
The shaped carrier particles which are used in the present
invention are characterized by a high surface area, generally over
100 square meters per gram, which is due to an internal pore
structure. This internal pore structure is well known in the
art.
According to the present invention, the carrier particles prior to
impregnation are immersed in a polar organic presoak liquid for a
time sufficient to fill substantially completely the pores of the
carrier. The quantity of presoak liquid is, of course, greater than
the total pore volume of the carrier being immersed. The total pore
volume of the carrier particles being immersed is computed by
multiplying the unit pore volume (i.e. cc/gram) by the quantity (in
grams) of carrier material. Immersion times of about 10 minutes are
sufficient in most cases to permit the presoak liquid to displace
the air in the carrier pores and to fill the pores completely; much
shorter times frequently are sufficient. Preferred presoak times
are in the range of about 10 minutes to about 2 hours; longer times
are permissible. Immersion temperatures ordinarily can range from
the freezing point to the boiling point of the presoak liquid. Room
temperature (about 25.degree. C. or 77.degree. F.) is quite
desirable in most cases. Lower temperatures increase the viscosity
of the presoak liquid and thereby reduce the rate of displacement
of the presoak liquid by the acid etching solution.
The presoak liquid must be capable of wetting the carrier material.
Carrier materials, such as sponge metals, which are not easily wet,
and nonwetting liquids such as mercury, are usually avoided. The
presoak liquid must also be capable of displacement by the acid
etching solution at a rate slow enough to permit control of the
extent of acid attack. Other criteria which are desirable in a
presoak liquid are: (a) chemical stability; (b) immiscibility or
only slight miscibility with the acid solution (to facilitate
removal of the acid solution without significant removal of the
presoak liquid); and (c) a volatility lower than that of water but
not so low as to hamper its removal during the drying and
calcination steps.
Aliphatic alcohols containing from 4 to 12 carbon atoms and
particularly primary aliphatic C.sub.5 -C.sub.10 monohydric
alcohols, are preferred presoak liquids. Normal decyl alcohol is a
preferred presoak liquid. Because of its greater viscosity it is
more slowly displaced than the lower alcohols. The etching process
is thus better controlled. 1-pentanol is a good presoak liquid. As
isomeric mixture composed predominantly of primary aliphatic
monohydric C.sub.6 alcohols, commonly known as "oxo alcohol," is
another good presoak liquid. An isomeric mixture composed
predominantly of primary aliphatic monohydric C.sub.8 alcohols,
which is also commonly called "oxo alcohol," is also a good presoak
liquid. In general, the C.sub.4 -C.sub.12, and especially the
C.sub.5 -C.sub.10, alcohols are good organic presoak liquids. Other
classes of organic compounds can also be used as presoak
liquids.
The above-named presoak liquids have been found particularly
desirable when alumina is the carrier material. There is some
variability in the choice of presoak liquids depending on the
choice of carrier material, since the readiness with which a
presoak liquid is displaced by the acid etching solution is
governed in large measure by the degree of interaction between the
presoak liquid and the carrier material, which in turn is
influenced by the chemical and physical properties of both presoak
liquid and carrier.
The preshaped carrier particles can be separated from excess
presoak liquid by any suitable method, e.g. removal of the carrier
particles from the body of liquid, or draining of the presoak
liquid from its container. At this point the pores of the carrier
are completely filled with presoak liquid, and some excess liquid
may be dragged out of the container of presoak liquid by the
carrier. The excess liquid may be drained or blotted from the
carrier if desired, although this is not necessary. However, it is
essential that the carrier not be dried at this stage. The carrier,
without drying is immersed in the acid solution.
The preferred acids must be capable of wetting and interacting with
the carrier material but being readily separated from the presoak
liquid. Strong acids are preferred since they can achieve the
desired etching of the carrier material. In general, the common
inorganic acids are desirable. These include hydrochloric acid,
sulfuric acid, nitric acid and phosphoric acid. Concentrations of
about 10% or less are especially preferred. Organic acids may also
be used if desired. The organic acid used should have a relatively
high ionization constant in order to insure sufficient etching
strength. Values for the ionization constant, Ka, of about
1.times.10.sup.-3 and higher are desirable. Suitable organic acids
include chloroacetic acid, trichloroacetic acid, maleic acid,
malonic acid and oxalic acid.
While the inventors do not wish to be bound by any particular
theory, it is believed that the improvement in activity for the
finished base-active component combination is due, at least in
part, to the controlled opening of surface-to-interior pores which
had been closed during the shaping process. This mechanism, of
course, should not be construed as defining the scope of
limitations of the invention, but rather, should be understood as
one possible explanation, recognizing that other mechanisms may
well play a major part in the effectiveness of this newly
discovered procedure.
Once the carrier material has been sufficiently etched, the acid is
washed away without substantially removing the presoak liquid. The
choice of wash liquid is dependent upon the selection of acid and
presoak liquid. Preferably, water is employed as a washing
solution, but acetone and lower molecular weight alcohols such as
methanol or isopropanol may also be used.
The impregnating solution contains, as its solute, a compound which
is decomposable into the desired active material. Thus, for
example, in the case of flue gas desulfurization sorbents where the
desired active material is cooper oxide, a copper salt such as
copper nitrate may be used as the solute. Where the desired active
material is another active material, e.g., iron, cobalt, nickel,
vanadium, chromium, zinc, cadmium, platinum or palladium, or a
compound (usually an oxide) thereof, a decomposable salt of the
desired metal is chosen as the solute of the impregnating solution.
Ferric nitrate, coabalt nitrate, nickel nitrate, platinum chloride,
and palladium chloride are examples of suitable decomposable salts.
In general, the desired active material is a metal, a metal oxide,
or a mixture of metals or metal oxides, and the solute or
decomposable compound is correspondingly a metal salt or a mixture
of metal salts. Suitable decomposable metal salts yielding
virtually any desired metal oxide are known in the art. The solvent
of the impregnating solution is usually water, which has the
advantage of low cost and high affinity for the usual carrier
materials. Thus, the preferred impregnating solutions are aqueous
solutions. However, solvents other than water may be used where
desired, provided the desired decomposable compound is soluble
therein. Suitable nonaqueous solvents include methanol, ethanol,
isopropyl alcohol, dimethyl sulfoxide, and acetonitrile.
The impregnated carrier material is dried and the decomposable
compound is converted to the desired active material. Usually,
drying and decomposition are separate operations, since most
decomposable compounds will be decomposed under normal drying
conditions. Calcination in an air atmosphere is a preferred means
of decomposing most decomposable compounds into the desired active
materials. Thus, for example, a copper salt such as copper nitrate
may be converted into copper oxide by heating the carrier particles
to a temperature of about 700.degree. F. to about 1200.degree. F.,
preferably 800.degree.-1000.degree. F., in the presence of air for
from 1 to 6 hours, preferably about 3 hours.
The preferred copper concentration on the finished sorbent is in
the range of about 2-10%, preferably 4-6% by weight.
Flue gas desulfurization sorbents comprising vanadium pentoxide on
silica can also be prepared according to this invention.
Where the desired finished product has a metal rather than a metal
oxide as its active material, as, for example, platinum on alumina
(which is a known hydrogenation and hydrocracking catalyst) the
metal compound (usually a metal oxide) obtained on drying and
calcination is reduced to the free metal. Suitable reducing agents
are known in the art.
Catalysts and sorbents prepared as described above can be used in
known catalytic, adsorption and cyclic chemical reaction processes.
Flue gas desulfurization, which is the preferred process of this
invention, falls into the third category.
Removal of sulfur dioxide from a waste gas, and subsequent
regeneration of the sorbent, can be carried out using a sorbent as
described above under known operating conditions. Thus, for
example, flue gas containing a minor amount of sulfur dioxide
(usually about 0.1-0.5% by volume of SO.sub.2 and typically about
0.2-0.3% by volume of SO.sub.2) plus some oxygen (usually about
1-4% by volume) is passed into contact with a fixed bed of the
above-described surface impregnated sorbent at a space velocity of
no more than about 10,000 V/V/Hr., and usually about 1,000 to about
5,000 V/V/Hr., and at a temperature which is appropriate to the
particular sorbent material used. In the case of copper oxide on
alumina sorbents, the inlet temperature of flue gas as it enters
the bed is generally about 600.degree.-900.degree. F., preferably
about 650.degree.-800.degree. F. Slightly higher inlet
temperatures, e.g., about 700.degree.-1000.degree. F., may be used
when the sorbent comprises potassium oxide and vanadium pentoxide
on silica, which is another known flue gas desulfurization sorbent.
These temperatures are typical flue gas desulfurization
temperatures which are known in the art. The active material, e.g.,
copper oxide, reacts chemically with sulfur dioxide and oxygen. For
instance, copper oxide is converted to copper sulfate. The passage
of flue gas is stopped and the sorbent is regenerated when the
amount of sulfur dioxide in the effluent reaches a predetermined
level. For example, if it is desired to remove 90% of the amount of
sulfur dioxide contained in a flue gas, the sorption or sulfation
cycle is interrupted and the regeneration cycle is begun when the
total amount of SO.sub.2 in the effluent over a whole sorption
cycle reaches 10% of the total amount of SO.sub.2 in the entering
gas.
The sorbents of this invention can be regenerated with known
reducing agents and under known conditions. Suitable reducing
agents include hydrogen, carbon monoxide, mixtures of these two,
mixtures of either carbon monoxide or hydrogen (or both) with
steam, and aliphatic hydrocarbons such as ethane, propane, or the
like, either undiluted or mixed with steam. Methane is less
desirable than its higher homologues because it is less
reactive.
It is desirable to use regeneration temperatures which are
approximately the same as the desulfurization temperatures, e.g.,
inlet temperatures, or about 600.degree.-900.degree. F. when a
copper oxide sorbent is used. Since both desulfurization and
regeneration are exothermic, sorbent bed temperatures are somewhat
higher than gas inlet temperatures.
Sorbents prepared according to the present invention can withstand
numerous sorption-regeneration cycles before they must be
replaced.
This invention will now be described further by way of the
following examples, which examples are included for purposes of
illustration rather than limitation.
CONTROL A
Alumina saddles (surface area 221 square meters per gram; pore
volume, 0.53 cc. per gram) were allowed to air hydrate overnight.
(Weight dry basis 287.63 gm., weight wet basis 309.28 gm., ca. 7.0
weight percent water pick-up.) The saddles were then immersed in
161.8 cc. of a copper nitrate solution (0.3268 gm. of
CuNO.sub.3.3H.sub.2 O per cc. of solution), allowed to air dry
overnight and then calcined for 3 hours at 800.degree. F. The
percent copper was determined to be 4.2%. A portion of the above
sorbent was tested for flue gas desulfurization (FGDS) activity in
a one inch glass unit and showed a 4.1% copper utilization at the
90% SO.sub.2 removal level.
EXAMPLE 1
Alumina saddles, which were the same as in the Control A, were
soaked in a n-decyl alcohol solution, removed from the alcohol
solution and dipped in a 10% HCl aqueous solution for 45 minutes.
The acid dipped saddles were then washed several times with
deionized water, air dried overnight and then calcined for 3 hours
at 1400.degree. F. The saddles were allowed to pick up moisture
overnight and a 5.8% moisture pick-up was noted. Twenty-five of the
thus processed saddles were dried for 3 hours at 650.degree. F. and
tested for pill strength (PLST). The average pill strength was
determined to be 10.7 lbs.
Another portion (27.05 gm. Al.sub.2 O.sub.3 on a dry basis) was
copper impregnated as in the Control A to give 4.6 weight percent
copper. The resultant sorbent was tested in a 1 inch glass under
conditions essentially as in the Control A and showed a 7.9% copper
utilization at the 90% SO.sub.2 removal level. The test conditions
were as follows:
60 cc. sorbent charge
3000 V/Hr./V
2700 ppm of SO.sub.2
650.degree. f. temperature
EXAMPLES 2-4
Alumina saddles, as in Example 1, were similarly presoaked in decyl
alcohol and dipped in 10% HCl. After dipping the saddles were
washed with deionized water until the washings gave only a slight
chlorine test. The washed saddles were oven dried overnight at
230.degree. F. and calcined for 3 hours at 1400.degree. F. Pill
strengths for varying dip time and compared with a control are
shown in Table I.
TABLE I ______________________________________ Dip time Change
Desig- Sorbent Presoak in PLST in nation type Alcohol 10% HCl (AV)
lbs. Strength ______________________________________ Control B
Alumina None None 13.2 -- Saddle Control C Alumina None 45 mins.
9.4 -29% Saddle Example 1 Alumina 1-decan- 45 mins. 10.7 -19%
Saddle o1 Example 2 Alumina 1-decan- 30 mins. 13.0 -2% Saddle o1
Example 3 Alumina 1-decan- 20 mins. 14.3 +8% Saddle o1 Example 4
Alumina 1-decan- 10 mins. 12.2 -8% Saddle o1
______________________________________
The activity gain achieved in accordance with the instant invention
is shown in Table II.
TABLE II ______________________________________ Dip Time % Cu
Utilization at Sorbent in 10% HCl % Cu 90% SO.sub.2 Removal
______________________________________ Control A None 4.2% 4.1%
Example 1 45 mins. 4.6% 7.9%
______________________________________
CONTROL D
Alumina rings (surface area, 174 square meters per gm.; pore
volume, 0.55 cc. per gm.) were allowed to hydrate in the air
overnight after a prior calcination for 3 hours at 1400.degree. F.,
resulting in a water pick-up of 6.6%. The hydrated rings (339
grams) were impregnated with a copper nitrate solution (0.327 gm.
Cu(NO.sub.3).sub.2.3H.sub.2 O per cc. solution), air dried
overnight and then calcined for 3 hours at 800.degree. F. The
percent copper on the alumina was 4.3%. A portion of this sorbent
was tested for FGDS activity in the 1 inch glass unit.
EXAMPLE 7
Alumina rings (as in Control D) were soaked in decyl alcohol,
drained and immersed in a 10% aqueous HCl solution for 45 minutes.
After washing thoroughly with water and drying overnight, rings
were calcined for 3 hours at 1400.degree. F. The rings were
impregnated with a copper nitrate solution, as in CONTROL D. The
percent copper on the alumina was determined to be 4.8%. The "acid
etched" sorbent was then tested for FGDS activity and the results
are shown in Table III.
TABLE III ______________________________________ Presoak 90%
SO.sub.2 Removal in Diptime Cu-Util- Sorbent Alcohol Wt.% Cu 10%
HCl B.T.Min. ization ______________________________________ Control
D None 4.3 None 5.7 9.1% Example 7 Decyl 4.8 45 mins 7.5 11.4%
Alcohol ______________________________________
* * * * *